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Calculators: Desktop: Hitachi KK221B

(c) Emil Dudek 2011

Size (approx): 113mm (max) x 169mm x 38mm  (w,h,d)
Weight 472g including rechargeable batteries


6V DC, Sealed unit Ni-Cd 4.8V battery pack (BP-01).  Also accepts adapter (AD23, 6V 1.5W).  Socket is on right side in the middle and is centre positive.  The rechargeable battery pack forms an inherent part of the case at the top rear.  Charging time is quoted as 16 hours to give 3 hours use.  A unit for inserting 4x AA batteries was also available. Quoted lifetime is 7 hours (alkaline) and 3 hours (manganese).
Case: Large slightly tapering cream plastic case, matt on the front, smooth on lower half.  Oversized green plastic display filter wraps over the top.  Silver painted logo, brand and model number has worn well as it is engraved into the filter.  Raised letters above the switches are not very clear.  Chunky long travelling buttons which make a hollow clunking sound.  Dark grey keys have white red or blue labels.  Just about fits in the hand even though it is a desk top calculator.
Display: 8 digit green VFD with an additional symbol cluster for negative, memory and overflow indication
Features: 4 function calculator with percentages, square roots, powers, 12 digit capability, display shift, switched total, switched constant and fixed decimal mode.  
Age: 1973
Manufacturer: Hitachi Ltd, Tokyo, Japan.  Serial No. P18911402 (pictured) also had P752374274.  Other serial numbers seen on the web:  P189323183, P189303065.


Lovely solid feeling early Hitachi calculator.  A dry-cell compartment was also available for 4 AA cells.  Keys feel like the old large-sized late 60s desktops.  The logic is basic with some odd functions and lack of recovery.  Original hard case (125mm x 185mm x 50mm) is red felt lined, strap and popper closing with handle.  It also has a silver painted Hitachi logo.  There is even a hole so that the adapter can be plugged in without removing from the case.

Components: 1 x IC: Hitachi HD3576 3M2 (date code December 1973) 28 pin DIL, 0.6" width black plastic
1 x IC: IC6294 739 (9th month? 1973) 22 pin DIL, 0.6" width plastic block
1 x IC: IC6297 739 (9th month? 1973) 24 pin DIL, 0.6" width plastic block
1 x IC: IC5403 739 (9th month? 1973) 16 pin DIL, 0.3" width plastic block
1 x IC: Hitachi HD3233P 3L5  (date code November 1973) 16 pin DIL, 0.3" width black plastic
1 x IC: Hitachi HD3213P 3L4  (date code November 1973) 16 pin DIL, 0.3" width black plastic
1 x IC: Hitachi HD3253P 3L1  (date code November 1973) 16 pin DIL, 0.3" width black plastic
1 x 8+1 digit VFD single tube, round face 9-CT-01 Futaba 3L (date code November 1973) (ED: so they were buying stock at least one month ahead)
4 x transistors
10 x diodes
15 x capacitors
10 x resistors
2 x resistor arrays
1 x voltage converting transformer
1 x fuse
Boards: The keyboard assembly (KBT-220S-20) sits on top of the main board (Hitachi 121) and the whole internal group is held in place by a single screw going though both boards.  A further two screws can used to separate the keyboard assembly from the main board which make electrical contact through a 24-way edge connector.
Construction: Remove the single screw from the rear (don't lose the two washers). Pop the two lugs either side of the display first by pressing in the rear section of the case, there are another two lugs at the bottom, and the front panel will then lift off.  Be careful - these instructions can not be held liable for any damage that you do to your example.

Logic comments: (CE) is used to cancel and entry whilst (C) clears the whole calculator.
Input overflow is suppressed, keying in a thirteenth digit is ignored
You can work with up to 12-digit numbers and use the display shift (<>) key to toggle between most and least significant parts, if a number is greater than 8 digits the display without the decimal point is the most significant part
When switched on the decimal point mode defaults to fixed zero decimal points. To select between 0 and 7 fixed decimal points use the first switch to select "DS" then press a number (8 and 9 act as 7) then switch back to the middle position "." for operation. If you select 5 decimal points then 4+5 gives "9.00000"
Negative numbers are flagged by "-" in the ninth (far right) symbol cluster
Overflow and underflow is flagged by the shifted result and a "?" in the ninth (far right) symbol cluster and is not recoverable
Divide by zero is flagged by no digits shown and a "?" in the ninth (far right) symbol cluster and is not recoverable
The logic is semi-RPN (Reverse Polish Notation), so to do 8-6 key in (8)(+=)(6)(-=) to give "2"
Constant function is switched using the "K" switch and is for multiplication and division only.  Interestingly you can use the constant to find powers and square roots: square root of three is (3)(/)(+=) with K on.
The basic memory is selected by using the main switch to select "S" (sigma), Then the result of every (+=), (-=) and (%) key is accumulated to memory and recovered/cleared by using the (T1) key.  This is also interesting as the "T" was commonly used for "Total Accumulation" before this model and the "1" implies there are more than one memories (which in this case there are not).
If the contents of the memory are non-zero a "M is shown in the ninth (far right) symbol cluster
Overflow or underflow in memory is flagged by a "?" in the ninth (far right) symbol cluster and is not recoverable, but the original memory can be extracted
It suffers the negative zero bug: key in (1)(+=)(2)(-=) to give "-1" now add (1)(+=) to give "-0"
It suffers the divide to negative zero bug, any negative number repeatedly divided by ten will eventually result in "-0"

(c) Emil Dudek 2011 Hitachi KK221B Calculator

Once the calculator is open and the keyboard assembly is removed you can see the extent of multiple ICs that is typical of such an early model.  Although the date codes point to late 1973, I believe that this model must have been designed at least a year earlier due to the large variation in the serial numbers.  The blue bar to the right is the edge-connector terminal to the keyboard assembly. The instruction manual measures 110mm x 150mm (w x h) and its 16 printed pages are in red and black.  Simple but essential instructions are given for the somewhat strange, but flexible logic.
Quote: "Congratulations on your wise decision to purchase this Hitachi Cordless Desk-top Electronic Calculator".

(c) Emil Dudek 2011 Hitachi KK221B Calculator

A useful section from the manual defining the keys in "Hitachi speak".  The "Display Exchange Key" is used to switch between the most and least significant components of the possible 12-digit number. A section from the manual showing the the dry cell options.  The rechargeable battery pack included the cover. The "knob" is more of a push-tag.

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